My girlfriend tried that last year when she was a bridesmaid. She can't remember the name of the product but it was v expensive. After a few hours in a hot environment (dance floor) the cream starts to melt and the tattoos show through. (and you look like your fake tan is running)
Assuming it won't be noticeable in the photographs, the girly advice is to take some sort of shawl/light cardi top to wear over the shoulders when required. (that's what she's going to do next time)